feat(e2e): ajouter tests Playwright flux utilisateur core (login, workspace, palette, dashboard)

- e2e/flowdeck_e2e_final.spec.js: 4 tests E2E validés
  1. Login UI local (#email, #password, .btn-primary)
  2. Créer workspace local + entrer (modal .dialog-input)
  3. Ouvrir palette Ctrl+K et valider 'Créer une collection'
  4. Dashboard accessible
- e2e/ : package.json, playwright.config.js, install chromium

e2e/package.json

@@ -0,0 +1,15 @@
+{
+  "name": "e2e",
+  "version": "1.0.0",
+  "description": "",
+  "main": "index.js",
+  "scripts": {
+    "test": "echo \"Error: no test specified\" && exit 1"
+  },
+  "keywords": [],
+  "author": "",
+  "license": "ISC",
+  "devDependencies": {
+    "@playwright/test": "^1.63.0"
+  }
+}